Separation of oil and water has been a worldwide challenge for some time. Oil-water separation is necessary due to increasing environmental awareness and regulations. Also, the production of industrial wastewater and accidental spillage of oil leads to a need for oil-water separation.
Certain efforts to increase the effectiveness of oil-water separation have involved the creation of devices that have hydrophobic-oleophilic (i.e. oil-removing) surfaces or hydrophilic-oleophobic (i.e. water-removing) surfaces. However, oil-removing surfaces tend to foul easily and become blocked by oils. These oils adhere to the surfaces and are hard to remove. This greatly affects the separation efficiency.
Substrates that have been previously studied for oil-water separation include polymers, such as polytetrafluoroethylene (PTFE), polyethylene, and polyurethane; metals, such as stainless steel and copper; ceramics, such as glass and manganese oxide; and others, such as filter paper, textile, and silicon. These have been in the form of fibers, meshes, foams, or surfaces. Certain embodiments of these substrates offer inferior properties, such as low flexibility and poor mechanical stability. Hydrophilic-oleophobic surfaces have been incorporated into certain embodiments of these substrates; however, the resultant substrates have not yet been used for oil-water separation.
Altering the wettability of a surface also affects the oil-water separation. The wettability of a surface can be changed by using surface modification techniques in order to achieve antifouling surfaces. Such techniques include vapor deposition, dip coating, spray coating, spin coating, and polymer grafting. A surface having superoleophobic properties generally requires the use of a hydrophilic material and hierarchical surface structures. Superoleophobic surfaces generally require the combination of surface chemistry and surface roughness properties.
The present invention employs zwitterionic species to modify the properties of filter media and provide an improved filter that provides more effective oil-water separation. Embodiments of the present invention offer one or more of the following improved properties: easy production, easy re-use or recycling, high resistance to organic contaminants (such as oil), high separation efficiency, low operating costs, and the use of highly roughed surfaces (e.g., nano-structured surfaces) is not necessary.